1. Field of the Invention
The invention pertains generally to mechanical actuator systems and is more particularly directed to motion transmitting linkages for linear actuators.
2. Prior Art
Actuators are mechanical apparatus which transform a pressure change (generally fluidic) into the physical displacement of a work element. In a linear actuator this work element is usually a piston rod that can be employed to produce useful work (force x distance) in operating switches, valves, or other mechanisms which require actuation.
There are at least two known types of linear actuator in wide use today. One type of linear actuator is referred to as a thermal actuator wherein the fluid pressure is increased by the application of heat to a thermally expansible material or the like within the actuator, as is disclosed, for example, in a U.S. Pat. No. 3,805,528.
The other type of linear actuator in wide use today is a fluidic actuator which is operated in response to a differential in pressure caused by pumping increasing volumes of fluid into a cylinder. The fluidic actuator can be either pneumatic or hydraulic depending upon the gaseous or liquid state of the actuating fluid. All of these devices are advantageous in that they provide a mechanical force useful over their working distance in a single direction.
However, there are instances in which rotational actuation is needed. Many times a valve will open by turning or rotating the check stem rather than by a linear pushing motion. Another particular need for rotary actuation is for pivoting the control arms of dampers in ventilation or heating systems. In the past, these rotational actuations with linear actuators have been accomplished by various linkages generally including a series of lever arms and pivots.
These complicated arrangements have been subject to mechanical wear and resultant play in the connecting elements. The mechanical play inherent or created in such linkages requires that the device be calibrated periodically or risk a non positive actuation of the rotating device.
Further, service and replacement of such parts is hampered by the relatively difficult disassembly necessitated by the physical connections of pivots and levers. This can be specifically problematic for heating and ventilating systems in vehicles which are typically mounted in rather inaccessible places such as a dashboard.